1. Field of the Invention
The present invention relates to an apparatus for scanning a sheet-like recording medium such as a stimulable phosphor sheet to read radiation image information of a subject that is carried thereon.
2. Description of the Related Art
There is known a system for recording radiation image information of a subject such as a human body with a stimulable phosphor, and reproducing the recorded radiation image information on a photosensitive medium such as a photographic film, or displaying the recorded radiation image information on a display device such as a CRT or the like.
When a radiation energy such as X-rays, xcex1-rays, xcex3-rays, electron beams, ultraviolet radiation, or the like is applied to a certain phosphor, it stores part of the applied radiation energy. When stimulating light such as visible light is subsequently applied to the phosphor, the phosphor emits light depending the stored radiation energy. Such a phosphor is referred to as a stimulable phosphor. A stimulable phosphor is usually used in the form of a sheet which is referred to as a stimulable phosphor sheet.
The above known system comprises a built-in image information reading apparatus which includes a recording section for temporarily recording radiation image information of a subject on a stimulable phosphor sheet, a reading section for photoelectrically reading the radiation image information recorded on the stimulable phosphor sheet by applying simulating light to the stimulable phosphor sheet, and an erasing section for erasing remaining radiation image information from the stimulable phosphor sheet after the recorded image information has been read, the stimulable phosphor sheet being circulated or moved back and forth in the apparatus. The known system also comprises an image information reading apparatus which includes a cassette loading section for loading a cassette which houses a stimulable phosphor sheet which bears recorded radiation image information of a subject, a reading section for reading the radiation image information from the stimulable phosphor sheet that has been removed from the cassette, and an erasing section for erasing remaining radiation image information from the stimulable phosphor sheet.
As shown in FIG. 9 of the accompanying drawings, the reading section of the image information reading apparatus comprises an auxiliary scanning feed system 1 for feeding a stimulable phosphor sheet S in an auxiliary scanning direction indicated by the arrow A, an optical system 2 for applying a laser beam L in a main scanning direction, which is perpendicular to the auxiliary scanning direction, to the stimulable phosphor sheet S that is being fed in the auxiliary scanning direction, and a light collecting system 3 for photoelectrically reading light which is emitted from the stimulable phosphor sheet S by the application of the laser beam L. The auxiliary scanning feed system 1 usually has first and second roller pairs 4, 5 spaced from each other by a given distance. The first and second roller pairs 4, 5 have respective nip rollers 4a, 5a that are movable back and forth in the directions indicated by the arrows.
In the auxiliary scanning feed system 1, a leading end of the stimulable phosphor sheet S is first fed by the roller pair 4 in the auxiliary scanning direction indicated by the arrow A, and the laser beam L emitted from the optical system 2 is applied in the main scanning direction to the stimulable phosphor sheet S. When the leading end of the stimulable phosphor sheet S approaches the roller pair 5, the nip roller 5a is displaced to cause the roller pair 5 to gently grip the leading end of the stimulable phosphor sheet S.
If the leading end of the stimulable phosphor sheet S is curled as indicated by Sa, then the curled leading end Sa cannot smoothly enter between the rollers of the roller pair 5. As a result, the radiation image information cannot efficiently be read from the stimulable phosphor sheet S.
For reducing the size of the image information reading apparatus, the stimulable phosphor sheet S may be fed vertically in the auxiliary scanning direction. When the stimulable phosphor sheet S is fed vertically, however, the read image tend to suffer unwanted irregularities because the stimulable phosphor sheet S that is fed vertically is liable to flutter.
It is a main object of the present invention to provide an apparatus for scanning a sheet-like recording medium highly accurately and efficiently while reliably feeding the sheet-like recording medium in an auxiliary scanning direction with a simple arrangement.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.